Several different abrasive-type cutting saws exist in the marketplace, each of which employ one or more abrasive or superabrasive materials, such as diamond, formed on a cutting segment that actually performs the cutting function. These conventional abrasive-type cutting saws include circular saws, frame saws, wire saws, chain saws, band saws, and others. The typical design of these conventional saws is to provide a unidirectional cutting motion, meaning that the cutting segments move only in one direction during the cutting process. This is particularly true when cutting hard materials, such as granite stone or quartzite.
It is well established that unidirectional cutting provides, as one advantage, high speed cutting. Moreover, unidirectional cutting allows the abrasive particles, namely the diamond grit, to be supported by the “bond-tail” of the matrix material left behind during the cutting action. Due to the lack of mechanical support, the abrasive particles or diamond grit will be knocked off easily by the impact force encountered. This is particularly true for those cutting members attached by mechanical means, such as by electroplating with nickel or by sintering with a metal matrix.
In the case of an impregnated diamond bead, placement of the diamond particles on the bead is difficult to maintain due to the physical characteristics of the diamond particles and the way they are mounted onto the bead. This is particularly true if cutting hard rock, such as granite. As such, it is crucial that a remnant of the metal matrix be left behind to reinforce each diamond particle and to maintain its proper placement on the bead during cutting.
With respect to the cutting of hard materials or substances, although unidirectional cutting has the advantage of enabling high cutting speeds and adequate abrasive particle support, there are several inherent deficiencies and limitations to unidirectional cutting. Moreover, unidirectional cutting is currently the only way to cut harder materials. In the case of circular saws and chain saws, the cutting depths are limited by the relative distance between the support or holding elements. In addition, these have a difficult time maintaining a continuously straight cutting path due to the often weak mechanical support from the holding elements. In the case of the band saw, the cutting span is very small. Furthermore, the abrasive particles are typically fixed to the cutting segment by electrodeposition, which is not strong enough to withstand the cutting of hard materials.
Only some of the above-identified abrasive-type saws allow parallel sawing of multiple blades. Chain saws and band saws typically cut with only a single blade, but circular saws and wire saws may comprise a plurality of blades. Of particular note, frame saws are capable of cutting with more than one hundred blades. Consequently, this is the most attractive saw for cutting and slicing large slabs or blocks of material. However, because frame saws move in a bidirectional or reciprocating manner, the “bond-tail” is lost. As a result, frame saws can only cut soft material, such as limestone because of the relatively weak support of the abrasive elements. If a frame saw, with its reciprocating motion, is used on hard material, such as granite, the abrasive cutting segments will fail. In other words, the abrasive particles will be ripped from the cutting segment as their support structure is not able to withstand the acting forces created during the cutting session as the cutting segment is applied to the hard material. Therefore, cutting hard materials remains a difficult task.
The most inexpensive way to cut hard materials is by sawing them with a steel blade frame saw that effectively achieves a grinding effect. During the cutting session, the steel blades are slid back and forth against the material while a slurry of iron grit and lime mud is fed into the cutting groove. The hard material is gradually eroded away by chemical reaction and mechanical abrasion. However, this is an extremely slow process and is also environmentally unfriendly. During operation, the steel blades grind away at the granite until it is cut. To illustrate how slow this process is, it takes four days to slice through 5 m2 of a granite block with a blade of this type. Other problems exist. First, it is difficult to keep the cutting path straight. Second, iron particles may produce stains on the material if the saw is exposed to humid weather for an extended period of time. Each of these lead to a significant amount of post-cut preparation and finishing. Third, because the steel blade is not cutting, but grinding, there is a substantial amount of vibration that can cause the often brittle material to crack. Fourth, the number of slabs that can be produced is limited, thus tipping the supply and demand scale against the consumer. Fifth, the slabs produced are relatively thick, thus limiting their use. For example, it is more desirable to use thin slabs when covering the exterior of a building as thicker slabs are heavy and expensive. Moreover, if the slabs could be cut large and thin, they could be used to replace wood and plastics as decorative coverings or linings. This is not currently possible. Although slow, and although there are several inherent deficiencies, this cutting system and method represents the most viable and economical way of cutting large blocks of hard materials that is available today.
Alternatively, in recent years abrasive-type wire saws have been utilized to slice through and cut granite blocks. Among the several different types of abrasive-type cutting saws, wire saws are a relatively new and unique addition to the family of abrasive-type cutting saws having originated from within the stone quarry industry, wherein the wire saws were created for the purpose of cutting and/or demolishing both stone and concrete in a more precise manner. Since their inception, wire saws have been modified and redesigned to provide specialized cutting in a wide variety of industries. As such, several variations of wire saws exist for use within a number of corresponding applications. As mentioned, one of the more common applications is in the stone cutting industry, wherein wire saws are utilized to cut concrete, stone, and other similar materials. Another common application is in the semiconductor industry, wherein wire saws are utilized to cut a silicon ingot to prepare a large diameter, thin-body silicon wafer used for manufacturing semiconductor devices.
The driving force behind the success of wire saws is the cutting wire itself and the technology used to create the cutting wire. Essentially, a cutting wire comprises a flexible steel carrier cable that is threaded through a series of steel segments or beads to which one or more abrasive materials is bonded or attached. The abrasive segments or beads are often called diamond beads or diamond peals. This is because the abrasive material most commonly used is diamond as it is the hardest and most durable abrasive material available. Indeed, diamond is widely used as a superabrasive on saws, drills, and other devices which utilize the abrasive to cut, shape and/or polish other hard materials. Diamond coated tools are particularly suited for applications where other cutting tools lack sufficient hardness and durability. For example, in the stone industry, diamond cutting tools are about the only type which are sufficiently hard and durable to make the cutting economical. Likewise, in the precision grinding industry, diamond tools, due to their superior wear resistance, are uniquely capable of developing the tight tolerances required, while simultaneously withstanding wear.
Typically, these diamond beads are made of steel cylinders having diamond particles or grits embedded on their exterior. There are several different sizes of diamond beads depending upon the intended application and the object to be cut. The most common sizes range anywhere from 6 mm in diameter to 10 mm in diameter. However, a smaller diameter diamond bead will narrow the kerf and the resulting loss of material than a larger diameter diamond bead.
The diamond beads are mounted in succession onto or about a flexible steel cable so as to be positioned at a fixed distance (e.g., approximately 40 diamond beads per meter) with respect to one another. The positioning of the diamond beads along the cable is pre-determined by the existence of steel, plastic, or rubber spacers lodged between each diamond bead. These spacers also serve as a protective coating for the steel cable, thus preventing its exposure to corrosive elements and prolonging its life.
Currently, there are three basic types of cutting wires. The first comprises a series of electroplated diamond segments or beads with compressed steel spring spacers therebetween. The second comprises a series of impregnated diamond beads, also with compressed steel spring spacers positioned therebetween. The third comprises a series of impregnated diamond beads with injection-molded plastic spacers positioned therebetween. From this, it is apparent that there are also two current primary bonding methods employed for manufacturing the various diamond beads. The method for creating an electroplated cutting wire involves attaching a single layer of diamond to the steel bead using electroplated nickel. The method for creating an impregnated bonding cutting wire involves pressing and sintering a diamond impregnated metal matrix to or around the steel bead, wherein the matrix comprises a blended powder metal alloy and diamond mixture, thus providing multiple diamond layers for more efficient and prolonged cutting. However, both of these types of conventional diamond beads are limited in their cutting ability when applied to hard materials, such as granite stone, as the diamond particles are mechanically coupled and subject to premature failure. Specifically, both the electroplated diamond beads and the impregnated diamond beads, produced as described, are only suited for unidirectional cutting of hard materials, and not for cutting such materials in a reciprocating manner. As discussed above with respect to frame saws, the cutting of hard materials in a reciprocating manner would effectively cause the diamond beads to fail.
Although many different types of wire saws exist, one conventional design that is frequently used to cut concrete, stone, and other hard materials comprises a loop of wire mounted on a series of pulleys, wherein the wire is further coupled to a flywheel that is driven by a hydraulic or electric motor. The wire, having a plurality of diamond beads, moves in a unidirectional, circular motion along its identified course at high speeds to perform the actual cutting function. While these wire saws present an alternative cutting system to the frame saws discussed above, there are still several significant disadvantages, thus they are seldom used. For example, wire saws are extremely expensive to manufacture compared to the lifespan of the cutting wire. In addition, the kerf from current wire saws is much larger than that produced by the frame saws, thus reducing the overall yield. Still further, although advantageous, current abrasive-type wire saws are unable to be operated in a reciprocating manner to produce a bi-directional cutting motion due to the limitations in the mounting of the abrasives. Although abrasives such as diamond have proven to be superior cutting particles, and although abrasive tools have long been used in numerous applications, including cutting, drilling, sawing, grinding, lapping and polishing materials, these have not been successfully utilized in wire saw in a reciprocating manner for the specific purpose of cutting hard materials.